Fracture and Viscous Behavior of Polypropylene Composites Coating Insulators for Deep Water Oil Pipelines
Ahossin Guezo, Yanhouide 1978-
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Over the past few decades, polymer composites are being used as subsea insulation coatings material in deep water oil pipelines. Failure of the insulation coating materials can significantly affect oil production. The major objective of this study was to characterize the physical and mechanical properties and quantify the effect of crack, strain rate and temperature on the visco-elasto-plastic behavior of the ductile polypropylene polymer (PP) with and without glass fillers in tension, compression, shear and bending. The density of the composite materials studied varied from 0.79 to 1.90 g/cc. The thermal conductivity of the coating insulators varied from 0.140 to 0.306 W/m.K. The effect of strain rate (ε ̇) and temperature (T) on the nonlinear visco-plastic stress-strain behavior, yield strength (σy), initial elastic modulus (Ei) and secant modulus at yield (Esy) of the materials (unfilled polypropylene, polypropylene with 65% glass filler and polypropylene with glass microsphere filler) was characterized and modeled. The tensile yield strengths of the materials varied from 3 to26 MPa. The rate of change in the tensile yield strength with temperature and strain rate were directly proportional to the yield strength and inversely proportional to the strain rate respectively. Crack growth and propagation in the multilayered polypropylene composite coating was investigated using the three dimensional Digital Image Correlation (3D DIC). Also the strain field (ε) development around the crack tip was investigated. A new concept based on Mode 1 strain rate amplification factor (γι) was introduced to model the behavior of polymer composite with crack that increased the tensile yield strength, initial modulus and secant modulus at yield but reduced the strain energy density, at yield and failure, and the ductility making the ductile coating materials stronger but more brittle. A three parameter constitutive relationship for polymer composites was developed to model the nonlinear visco-elasto-plastic and strain softening/hardening behavior of the polypropylene composites coating materials in function of strain rate (ε ̇) and temperature (T).